1. Technical Field
The present disclosure relates to a resonant converter apparatus. More particularly, the present disclosure relates to current balance in a resonant converter apparatus.
2. Description of Related Art
With advanced development of technology, more and more power applications are designed with high efficiency, high power density, low cost, etc., and thus resonant converters are widely applied. In high power applications, resonant converters are usually connected in parallel with each other and operate accordingly to deliver high output current, which has advantages for maintenance, and the reliability of the apparatus may be improved by using parallel redundancy.
FIG. 1A is a diagram illustrating a conventional resonant converter apparatus. As shown in FIG. 1A, resonant converters 12 and 14 are connected in parallel to a pre-regulator 10, and the pre-regulator 10 and the resonant converters 12 and 14 cooperate with each other to deliver high output current. However, when impedances of the resonant converters 12 and 14 are different, output currents of the resonant converters 12 and 14 are unequal. Although the output currents of the resonant converters 12 and 14 may become equal if the resonant converters 12 and 14 operate with different operating frequency, this would result in that ripples of the output currents of the resonant converters 12 and 14 cannot have a phase difference of 90°, thus causing a large ripple on current of an output filtering capacitor.
Furthermore, two or more resonant converters connected in parallel may output the same current if the symmetrical design or layout is utilized, but it is difficult to ensure a completely symmetrical layout since there are some inherent differences (e.g., different impedances) between circuits. Therefore, there is always an output current difference or unbalance between the resonant converters, which results in low efficiency and thermal loss of the apparatus and the loss for the resonant converter delivering high output current could be significant.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.